Chemicals, fertilizers and other particulates (in powder or granular form) are commonly applied to agricultural fields by transverse spreaders that cover a wide swath during each pass of the equipment. The particulate distribution system can be mounted on any form of land vehicle, such as a trailer, truck or specially designed self-propelled vehicle. Normally such vehicles will carry a particulates storage hopper, a transverse distributor for spreading the particulates, and a conveyor for moving particulates from within the hopper to the distributor. Because uniformity is necessary to effective spreading of chemical particulates about a field, a metering system for measuring and allocating flow of particulates to the distributor is either included within the distributor itself or is interposed between the conveyor outlet and the receiving distributor.
One form of distributor for spreading of particulates is a relatively simple spinner. One or more rotating spinners fling particulates onto the field surface as the material is dropped onto the spinners by a delivery mechanism or conveyor. However, the accuracy of distribution in this type of system is relatively crude. The field width which can be accommodated by use of spinners is definitely limited, since variations in delivery rate become increasingly pronounced as the width of the covered swath increases.
Mechanical delivery of particulates has been accurately achieved by mounting a transverse spreader hopper across a vehicle and providing a system of baffles, apertures, agitators and/or augers along its length. One example of such system is shown in U.S. Pat. No. 3,259,278, issued Jul. 5, 1966. A later improvement in such systems is disclosed in U.S. Pat. No. 3,680,741, issued Aug. 1, 1972. As illustrated in both patents, increaed width across the distribution system was achieved by untilizing foldable hoppers that can either be arranged at the sides of a vehicle for distributing particulates at positions alongside the vehicle for transport purposes.
More recently, field application systems have been introduced which use pneumatic distribution tubes to carry particulates outwardly to each side of a vehicle. These systems are illustrated by the equipment shown in U.S. Pat. Nos. 4,462,550 and 4,964,575. In these systems, metering of incoming particulates between vertical chutes leading to the tubes is achieved by mechanically flinging the particulate material by a centrifugal deflector. Other metering systems that have been commercially used in such systems involve metering rollers, star wheels and conveyor chains. In all these systems, the particulates are simultaneously directed into a plurality of chutes as a group. They deliver particulates to multiple delivery tubes in common metering mechanism. The required proportional flow to the individual tubes is attempted to be achieved by delivering a measuring amount of particulates across all of the tubes at the same time. However, the supposition that this will reslut in the same amount of particulates being dropped into each tube fails to take into account variations that occur due to vehicle speed, ground roughness, and the inclination of the supporting ground surface and vehicle carrying the system. While such systems might accurately meter the incoming rate of flow of the particulates to the distributor, they cannot assure that accurate proportional flow of particulates will be directed to the individual pneumatic delivery tubes under all operating conditions and desired rates of application that are typically encountered in field usage.
The change from mechanical to pneumatic distribution systems was dictated by a desire to reduce the operational weight of the wings or booms extending to the sides of the vehicle. In a pneumatic system, no particulate material is stored or maintained across the distributor. The distribution system is "dynamic"--all particulates that are in the distributor remain in motion once delivered to the pneumatic delivery tubes. In addition, the pneumatic tubes are lighter than the metering mechanism required in a mechanical system, thereby reducing the weight that must be supported across extended wings or booms. Finally in those instances where the wings or booms encounter a fixed object or pole while travelling in a field, the pneumatic tubes are much simpler to replace or repair.
One trade-off encountered when moving from a mechanical distributor system to a pneumatic system is that the pneumatic system typically discharges particulates at much wider spacings than have been used in comparable mechanical systems. Because the mechaincal systems used a common metering auger across the bottom of the distributor hopper, it was practical to discharge pariculates at 6 inch intervals across the system. After allowing for free fall of the particulates onto a field surface, this relatively close spacing assured substantially uniform application of particulates across the area being treated. Since each outlet along a pneumatic distributor system requires a separate pneumatic delivery tube, it is common to space the pneumatic outlets in the range of 30-36 inches apart from one another. The greater spacing is somewhat accommodated by the fact that the particulates are forcibly ejected from the delivery tubes by a flowing airstream, which permits the tubes to be provided with angular deflectors in an attempt to form uniform application patterns across the system. However, nonuniform flow of particulates through the individual delivery tubes will obviously impact a much wider swath across the field than would variations in delivery of particulates to the more closely spaced outlets in a mechanical system.
In order to assure more accurate and uniform distribution of particulates in a air distribution system, the present disclosure was directed to a system for individually metering the flow of particulates into each pneumatic delivery tube. A separate metering conveyor or auger is provided for each delivery tube, insuring that changes in vehicle inclination or in the rates of particulate application do not affect one delivery tube differently from one another. The result of this system has been a markedly improved uniformity of application across relatively wide field areas. The metering assembly also lends itself to a double stack of horizontally layered delivery tubes, permitting more tubes to be provided along the supporting wings or booms and allowing the tube outlets to be more closely spaced at intervals of 20 inches, as an example.